Borderline Personality Disorder (BPD) and Antisocial Personality Disorder (ASPD) are among the most serious, complex, and costly public health concerns facing the US healthcare and criminal justice systems. Both disorders begin to emerge by adolescence and are associated with increased risks for depression, substance abuse, self-injury, suicide attempts, and poor social, occupational, and academic outcomes.1-3, 18-25 In addition, both disorders may be particularly pernicious among young girls. Estimates suggest that up to 14% of adolescent girls in the community meet criteria for BPD, and as many as 10% of adolescent girls in the US general population engage in serious antisocial behavior.4-6,15 There is a need to identify features that might contribute to the etiology of these disorders to ultimately aid prevention and intervention efforts. Broadband risk factors that are common to both BPD and ASPD have been identified, 1 but the specific precursors that differentially predict the emergence of these disorders in girls are poorly understood. Interpersonal difficulties are core features of BPD and ASPD that may contribute to the manifestation and perpetuation of other features, including affective disturbance and mood-dependent, impulsive behaviors. Based on evidence suggesting that BPD and ASPD may be characterized by distinctive interpersonal patterns, I have developed the hypothesis that BPD and ASPD may have qualitatively different interpersonal precursors that are recognizable during childhood and that differentially predict the development of these disorders during adolescence. This proposal outlines a study designed to test this hypothesis using latent growth modeling methods in a large prospective study of inner-city girls followed longitudinally from ages 5-20 (the Pittsburgh Girls Study). The aims of this study are: 1) to identify distinctive developmental trajectories of early interpersonal processes from ages 5-14 that may function as precursors to BPD and ASPD features in adolescence; and 2) to determine the predictive validity of interpersonal precursors identified in Aim 1, and identify the magnitude and timing of the risk that they confer for the development of BPD and ASPD features from ages 14-20. The central hypothesis of this proposal is that, after controlling for common temperamental and environmental childhood risk factors for BPD and ASPD, a hypersensitive/inconsistent interpersonal style during childhood will confer specific risk for the development of BPD, and a callous/aggressive interpersonal style will impart specific risk for the development of ASPD. This study has the potential to describe and explain trajectories of development of BPD and ASPD in girls across critical periods of personality development and to identify the risk factors and precursors that are common and specific to the development and maintenance of these disorders in girls. This knowledge can be used to develop prevention and treatment efforts that target these specific processes. This research responds to Strategic Objective 2 of the NIMH Strategic Plan (Chart Mental Illness Trajectories to Determine When, Where, and How to Intervene). PUBLIC HEALTH RELEVANCE: Borderline Personality Disorder (BPD) and Antisocial Personality Disorder (ASPD) are chronic, debilitating, and complex psychiatric conditions that affect more than 3 million US adults annually and are associated with several negative outcomes, including high rates of morbidity and mortality, poor treatment response, and poor social, occupational, and academic outcomes.1-3 There is a critical need for research that addresses the developmental course of BPD and ASPD symptoms. The proposed study seeks to examine the common and specific interpersonal precursors to the development of BPD and ASPD features in adolescent girls using latent growth modeling methods, resulting in improved intervention efforts that target interpersonal precursors and that may have a higher impact during adolescence than in adulthood.